1. Field of the Invention
The present invention relates generally to the field of magnetic head positioning mechanisms for tape backup devices. More specifically, the present invention discloses a magnetic head positioning mechanism having a self-centering lead screw.
2. Statement of the Problem
In tape backup systems for personal computers, parallel tracks of data are recorded on a tape media in a data cartridge. The magnetic head must be positioned relative to the tracks on the tape such that the head gap centerline is within a prescribed dimensional tolerance of the recorded track center line. In order to maximize the data storage capacity of the tape, the separation between adjacent tracks has been minimized which in turn places severe tolerances on the accuracy of the head positioning system.
The highly competitive nature of the market in personal computer hardware has resulted in a dramatic decline in the price of most components over the past several years. This trend has placed competitive pressure on manufacturers of tape backup systems to continually reduce the costs associated with manufacture and assembly of these devices, without sacrificing performance or reliability. In response, manufacturers have attempted to simplify the mechanical design of tape backup systems to reduce the number and complexity of the components required to assemble each device. This tends to reduce the total cost of the components and also reduces the time and cost associated with assembly of the device. Finally, simpler mechanical designs tend to be more reliable, and therefore reduce warranty and repair costs, and also increase customer satisfaction.
A number of magnetic head positioning mechanisms have been used in the past in tape systems, including the following:
______________________________________ Inventor Patent No. Issue Date ______________________________________ Zarr 4,313,143 Jan. 26, 1982 Cannon et al. 4,943,877 July 24, 1990 Baheri Re. 33,661 Aug. 13, 1991 Baheri 5,132,858 July 21, 1992 ______________________________________
In U.S. Pat. No. Re. 33,661, Baheri discloses a head positioning assembly in which a magnetic head 14 is mounted on a carriage 20 having a bore 36 therein. The carriage slides along a stationary guide rod 40 extending into the bore. A lead screw 24 is directly driven by a stepper motor 26 and is threaded into a follower nut 76. This nut 76 is keyed to the head carriage so that rotation of the lead screw moves the carriage along the guide rod. A torsion spring 52 engages the carriage and provides a force to bias the carriage so as to eliminate any undesired clearance between the carriage and the follower nut and between the carriage and the guide rod. The spring force is applied at an angle relative to the axis of motion of the carriage. The spring is oriented so that the total force directed parallel to the axis of the motion of the carriage remains constant over its range of motion. The top surface 82 of the follower nut 76 is rounded to allow the carriage to "float" on the nut, or move freely in virtually all directions while still maintaining contact with the follower nut 76.
Zarr discloses a magnetic head positioning mechanism for a multi-track tape cartridge system including a stepper motor 38 that directly drives a lead screw 40. A screw follower 42 threaded on the lead screw is used to incrementally move the head in a direction transverse to the path of the magnetic tape. The follower 42 also includes a projection 44 that interacts with a guide stud 46 so as to allow only linear motion of the follower 42 along the lead screw 40.
Cannon et al. disclose a tape head positioning system for a tape cartridge backup system having a stepper motor 30 with a lead screw 50 and a follower nut 60 threadedly engaging the lead screw. The follow nut has a slot 62 for receiving one end of a lever arm 70. The other end of the lever arm engages in a slot 92 in the head mounting assembly 90 carrying the tape head 150. The lever arm is pivoted about a fulcrum at a predetermined location between its ends. The position of the fulcrum determines the mechanical advantage of the system, thereby allowing an inexpensive, coarser stepper motor to effectuate fine adjustments of the tape head.
In U.S. Pat. No. 5,132,858, Baheri discloses a magnetic head positioner in which the lead screw 12 passes coaxially through a hollow cylindrical tube 13. Two slots are provided through the peripheral wall of the tube. A floating nut 14 is threaded on the lead screw 12 to translate as the lead screw is rotated by the motor assembly. The floating nut 14 is provided with two outwardly extending wings 24, 25 which fit within the slots provided in the tube. A carriage assembly is secured to the magnetic head and includes a tubular structure 26 having two slots. The tubular structure 26 is placed over the slotted tube 13, floating nut 14, and lead screw 12 with the wings 24, 25 of the floating nut 14 extending through the slots and with the closed ends of the slots resting against the wings of the floating nut 13 to maintain the head position in dependence upon the position of the lead screw 12.
None of the prior art references uncovered in the search show a magnetic head positioning mechanism in which the lead screw is supported between its base and the follower nut in a self-centering fashion to minimize the effect of misalignment and to simplify assembly of the device. In particular, both the base of the lead screw and the follower nut threaded on the upper portion of the lead screw are allowed to pivot and self-align. This feature reduces the dimensional tolerances that must be observed in manufacturing the head carriage, follower nut, lead screw, and chassis. It also significantly simplifies assembly and repair of the device and therefore reduces assembly and repair costs.